Polyurethane elastomer is one of the most popular thermoplastic elastomers, which is also referred as TPU. TPU not only possesses excellent thermoplastic processing workability, but also has an elasticity similar to rubber. Therefore, it can be utilized to manufacture many different articles, such as parts of sporting goods and electrical appliances, and fibers, by injection molding, compression molding, blow molding and extrusion.
The most commonly known conventional manufacturing process of the elastic fiber is the dry-type method of DuPont, which comprises the steps of: first, producing a composition of polyurethane (PU) elastomer; second, extruding an organic solution of the elastomer from a spinning orifice; and third, removing the organic solvent by blowing heated nitrogen to the extrudate to form the elastic fiber. The volatilization of the organic solvent such as dimethyl formamide (DMF) and dimethyl acetamide (DMAc) causes serious drawbacks of the above dry-type method, because the solvent vapor is very hazardous to human health and generates a great pollution to the environment. The manufacturer must invest a huge sum of money to recover the solvent; therefore the dry-type method unreasonably increases the production cost of the elastic fiber that adversely affects the marketing development and competition.
In recent years, Japanese companies developed a new technology to manufacture elastic fiber by melt spinning, such as Nisshinbo, Kanebo and Kuraray. The Japanese method is different from the above DuPont's method by eliminating the use of organic solvent, so that the manufacturing cost thereof is relatively lower than the DuPont's dry-type method. However, the raw material, polyurethane, has poor thermal properties. So that the physical properties of the polyurethane will be adversely affected after high temperature melt spinning. Furthermore, the elastic fiber has to be subjected to high temperature and hydrolysis conditions in finishing processes such as dyeing, so that the elastic fiber produced by the melt spinning method contains much more restraints in application and has lower physical properties than the elastic fiber made by the DuPont's dry-type method.